UDS-D prevents a partner system from interpreting a long delay in the processing of a DML statement as a line failure or a failure in the corresponding partner system.
When the UDS-D task receives a DML statement from a remote application program, it sends time acknowledgments back to the remote application program. These time acknowledgments indicate that the DML statement is still being processed by the server task (see figure 25). The UDS-D task sends the time acknowledgments to UDSNET, the distribution component in the user task that handles communication requirements.
The time acknowledgments are sent at periodic intervals, which depend on the DBH load parameter PP CHCKTIME.
Figure 25: Monitoring the logical connection to the remote application program
UDSNET waits for a message from the remote UDS-D task for a fixed time period, which depends on the value of PP CHCKTIME.
If this time period expires without a message being received from the remote UDS-D task and without any message indicating a lost logical connection, UDSNET clears the connection to the remote UDS-D task, and then reconnects and repeats the last DML statement.
If UDSNET does not receive a response again, it rolls back the transaction, and status code 122, “Transaction prematurely canceled”, is sent to the application program.